1. Field of the Invention
The present invention relates to improvements in an idle engine speed control apparatus which is connected to an internal combustion engine of an automotive vehicle.
2. Description of the Prior Art
Various types of an idle engine speed control apparatus have been proposed in order to meet requirements of maintenance free and exhaust gas emissions. One typical apparatus which automatically controls an idle engine speed at a target value is disclosed, in "Nainen Kikan (Internal Combustion Engine)", Vol. 27, No. 341 published by Co. Sankaido in March, 1988. Such an idle engine speed control apparatus is provided with an idle control valve 3 in a bypass passage 2 as shown in FIG. 6. The bypass passage 2 is formed to bypass throttle valve 1 in an intake passage (no numerals). The idle control valve 3 is directly controlled by a signal from a control unit 4 so that the idle engine speed is feedback-controlled at a target value of the engine speed.
However, difficulties have been encountered in this type of conventional control apparatus, the supply timing of supplemental air is delayed by virtue of a space formed in a collector 5 downstream of the throttle valve 1. Since the supplemental air is not momentarily delayed before being supplied to the combustion chamber, the engine further lowers its idle engine speed during the delay time, thereby causing problems such as a sudden engine stop or lack of stability in the idle engine speed.